156 PROCEEDINGS OF THE ACADEMY OF [1888. 



Suppose, however, that the slider be pushed from B only as far as S, 

 then the current entering at A will divide into two branch currents 

 passing respectively to S and X. The one branch current on reach- 

 ing S will subdivide again into two currents one of which will return 

 through S B to the Daniell element the other passing into the galva- 

 nometer G and deflecting the needle to the left for example, supposing 

 it to be unopposed by the current which we shall see passes into the 

 galvanometer G in the opposite direction from T. The other branch 

 current on passing through X, the muscle or nerve whose resistance 

 is to be determined, on reaching T will similarly divide into two 

 currents, one of which passing through the resistance box R will re- 

 turn through B to the Daniell element ; the other passing into the 

 galvanometer will deflect the needle to the right supposing it to be 

 unopposed by that passing into the galvanometer G from S in the 



opposite direction. The resis- 

 tance box just referred to. Fig. 

 2, is so called on account of 

 its offering a resistance to the 

 passage of an electrical cur- 

 rent the amount of resistance 

 offered being determined by 

 Pj^j 2 ^"^^^-"^ the number of plugs out. Let 



us suppose for example, the slider being at B, that we make 

 the resistance box offer a resistance of 100 ohms (1) by taking 

 out the plug numbered 100, Fig. 2 a, the effect of this will be 

 that of the current which would otherwise return through R to the 

 Daniell, part now passes into the galvanometer and deflects the nee- 

 dle to the right. Let now, however, the slider be moved from B to S, 

 that is to exactly the middle of the wire or to its 500th division, it 

 will be observed that the needle of the galvanometer G is deflected 

 back to zero, proving that of the current which, when the slider was 

 at B, returned to the Daniell element, part now passes into the 

 galvanometer G opposite in direction to that passing in the galva- 

 nometer from T, but with an equal electro-motive force since the 

 needle of the galvanometer is brought to zero. Let us suppose in 

 order to illustrate graphically the relation of the forces involved in 



An ohm is the resistence offered by a copper wire 1 mm. in diameter and 

 46'25 mm. in length. 



